U.S. Pat. No. 4,731,772 and U.S. Pat. No. 4,757,197 describe the integration of a semiconductor laser device and a photo-detector in the same package for reading information from compact discs (CD). At that time optical heads used in compact disc players had only one laser. However, U.S. Pat. No. 4,757,197 anticipated that someday such a reading device might have two semiconductors in the same package.
FIG. 1 shows the two lasers package from U.S. Pat. No. 4,757,197. Two laser chips 94 and 96 are mounted on a first surface of a heatsink 102. Two detectors 98 and 100 are mounted on a surface normal to the first surface of the heatsink 102. Polarization filters 104 and 106 are used to separate the signals from the separate detectors. A hologram (not shown) diffracts the returned light, which originated from laser 96, to detector 100. The returned light which originated from laser 94 is diffracted to detectors 98 and 100.
With the development of digital versatile disks (DVD), the pits on the disks can only be read using a short wavelength laser. However, the recordable compact discs (CD-R) contain a dye which can only be read by a long wavelength laser. Consequently, all the optical heads used in DVD/CD players today contain two lasers, one has wavelength near 780 nm and the other has wavelength near 650 nm. U.S. Pat. No. 5,717,674, which issued in 1998, described a similar concept for construction of an integrated laser/detector device containing two lasers. This prior art is shown in FIG. 2. Laser 201 is the short wavelength laser. Its returned light from the high density recording layer is diffracted by hologram 204 to detector 207. Laser 202 is the long wavelength laser. Its returned light, after being reflected by the CD recording layer, is diffracted by the same hologram 204 to detector 208. Objective lens 205 is used to focus the laser light on the surface of the recording layers. As shown in FIG. 2, the high density recording layer is separated from the CD recording layer by a distance of 0.6 mm. Aberration correction plate 206 is inserted below the objective lens when the information on the CD recording layer is being read. The thickness t of the grating 203 is selected so that its structure is invisible to laser 201. The thickness T of hologram 204 is selected to have more light returned to detector 207.
U.S. Pat. No. 5,717,674 differs from U.S. Pat. No. 4,757,197 in that the detectors 207 and 208 are on the same side of the lasers, whereas the detectors 98 and 100 of the '197 patent (FIG. 1) are on either side of the lasers. Furthermore, detectors 98 and 100 are on the same plane relative to the optical axis whereas detectors 207 and 208 are on different planes.
U.S. Pat. No. 6,211,511 is another recent patent describing an integrated laser/detector device for DVD optical heads, which is shown in FIG. 3. The integrated device 300 contains a laser chip 310, which can emit two wavelengths of light. On either side of the laser chip 310 are detectors 330a and 330b. It also contains a hologram 320 to diffract the returned light from the disc to the respective detectors. The light emitted by the laser with a short wavelength has a large cone as shown by the solid lines. After being collimated by lens 340, it is focused by objective lens 350 to disc surface 360a. Light reflected by surface 360a is diffracted to detector 330a. 
Light with a longer wavelength is reflected by surface 360b and is diffracted by hologram 320 to detector 330b. The concept in U.S. Pat. No. 6,211,511 is similar to U.S. Pat. No. 4,757,197.
All three aforementioned patents contain one hologram lens, which can only have its pattern adjusted to align one laser to one detector. After that has been done, the integrated device relies on mechanical accuracy to insure that the light from the second laser is directed to the second detector. Therefore the placements of the detector and the laser chip must be very accurate. U.S. Pat. No. 5,285,062 describes a single laser device and has a hologram lens which can be rotated to make a manufacturing adjustment so that the returned beam hits the photodetector. It is the intention of this present invention to describe an integrated laser/detector device with dual lasers in which the returned light beams from the disc can be individually aligned to the respective detectors.
In the three aforementioned patents the lasers emit beams parallel to the optical axis of the objective lens. However, U.S. Pat. No. 5,727,009 shows a laser emission which is reflected by a 45 degree prism so that the laser beams after passing through the prism are parallel to the optical axis of the objective lens as shown in FIG. 4. A laser chip 404 is mounted on a submount 403 which also contains a photosensitive element 403a. Submount 403 is attached to a base 402 which has a cavity 402e for the insertion of a mirror 406. A multiple element detector 405 is attached on one side of the mirror 405 opposite to the laser chip. As can be seen in FIG. 4 the laser emission is reflected upwards by mirror 406 through a diffractive component 431. On the lower side of this diffractive component 431 is a grating 407a, which splits the laser beam into three beams. A holographic lens 408a is fabricated on the top surface of the diffractive component 431. The returned beam from the disc is diffracted by holographic lens 408a to the detector 405. It is noted that the mirror 405 is fixed relative to the position of the laser chip 404 and the detector chip 405.